1. Field of the Invention
This invention relates to an ink ribbon cassette for impact type printers such as a typewriter or a wire-dot printer.
2. Description of the Prior Art
An ink ribbon cassette to be used for the impact type printers such as a typewriter or a wire-dot printer usually contains in its case an endless type ink ribbon which is held between a pair of knurled rollers which drive the ribbon by means of friction. The volume of ink being limited to the volume impregnated in the ink ribbon beforehand, long term use can not be hoped for. In order to remedy this shortcoming, there are ink ribbon cassettes made with an ink roller made of an ink soaked plastic sponge installed in its case, to which the ink ribbon is made to contact while in use for printing.
In this case, only the limited quantity of ink that was impregnated in the ink roller could be fed to the ink ribbon, which resulted in failure to sufficiently attain the intended long term use. In another prior art, in order to give a proper tension to the ribbon, a leaf spring was provided as a friction member to keep the ribbon pressed to the inner surface of the case. At the time of manufacture in this case, the tape had to be set in position to get through the gap between the spring and the case by holding the spring in bended state in resistance to its elastic strength. This necessitates a critical production step of placing the ribbon to get through the passage while holding the spring in bended condition.